This invention relates to helicopters, and more particularly to the improvement of the helicopter torque control system.
At low to medium forward speeds, helicopter performance is limited by the effectiveness of the means for counteracting main rotor torque and controlling sideslip air loads. In order to provide sufficient torque control and adequate sideslip ability, most prior designs have employed a combination of tail fin and a relatively large, power consuming, tail rotor. The problems associated with the use of this type tail rotor are well documented in the prior art. The foremost problem is the hazard presented by the tail rotor, particularly to ground personnel. Additionally, in military helicopters, the tail rotor is vulnerable to combat damage which can result in catastrophic loss of control of the helicopter. Also, the reliability and maintainability problems of a tail rotor, with its gearboxes, bearings, and drive shafts, are severe. Further, during high speed flight the tail rotor requirement can be reduced, since yaw control can be provided by aerodynamic surfaces. However, the typical tail rotor continues to use excessive engine power and to produce adverse drag effects.
In order to avoid these problems, efforts have been made to eliminate tail rotors. In U.S. Pat. No. 4,200,252 (Logan) and earlier referenced patents, helicopter anti-torque systems are disclosed which employ the principles of fuselage circulation control using the main rotor downwash. These inventions describe how exhaust or other engine-driven air may be ducted into the helicopter aft fuselage section and then be injected tangential to the fuselage in order to induce more circulation. This increase in circulation is achieved by use of main rotor downwash to produce additional lateral forces on the fuselage which oppose main rotor torque.
However, it is established in prior art that main rotor downwash does not flow over the fuselage during high speed flight. The forward velocity of the helicopter moves the fuselage clear before the wash can reach it. Viewed from within the helicopter, the downwash pattern appears to have a large rearward horizontal component. Thus, a supplemental means of directional control, other than circulation control alone, is necessary. These supplemental means include tail rotors, aerodynamic fins, and reaction jets.
Two U.S. patents specifically address circulation control, Logan supra and U.S. Pat. No. 3,807,662. Both of these patents contemplate increasing the favorable lateral forces on the helicopter fuselage. These types of devices result in increased complexity and weight. The ducting, plenum and nozzle arrangements require considerable redesign and modification of the helicopter. Further, the possibility of mechanical failure and the increased vulnerability in the case of a military helicopter remain inherent deficiencies.
Accordingly, it is an object of the present invention to provide upper and lower fuselage strakes which will beneficially alter the air flow around the helicopter tail boom.
It is a further object of the present invention to reduce the load requirements on the helicopter torque control means.
Yet another object of the invention is to reduce the size of the helicopter torque control means by using fuselage air loads to provide part of the needed torque control.
A further object of the invention is to increase helicopter sideslip ability by controlling air flow circulation around the fuselage.
Another object of the invention is to provide a retraction/extension mechanism whereby the strakes may be positioned for optimal performance.
A further object of the invention is to prevent interference between aerodynamic surfaces by providing segmented strakes.
Another object of the invention is to provide improved reliability and maintainability for the helicopter torque control means by reducing power and load requirements.
Still another object of the present invention is to improve helicopter performance through increased speed, increased fuel savings and increased load capacity by decreasing power required from the torque control, by decreasing drag inherent in the torque control, and by reducing weight of the torque control means.